The bout opened the preliminary card of Saturday’s UFC on FOX 6 event, which took place at Chicago’s United Center. It streamed on Facebook prior to additional prelims on FX and the FOX-televised main card.

Jiu-jitsu specialist Mitchell signaled his intention to make the fight a standup affair as he worked a jab early against Thoresen. Neither man landed much of note, though a left hook landed clean for Mitchell on several occasions. Midway through the frame, Mitchell walked straight into a counter punch and was forced on the defensive. The action intensified as the round drew to a close, with both men battering each other with big shots. Mitchell, however, remained the more active fighter.

Advised by his corner to tighten up his striking, Mitchell pursued and then rocked Thoresen with a flurry early in the following round. Crumpling to the mat, the two worked for position as Thoresen battled to recover his wits. Mitchell wound up on top and worked ground and pound before attempting a heel hook. Unsuccessful, he gave up position, but he came very close to securing a rarely seen gogoplata. Thoresen escaped, only to struggle with follow-up sub attempts from Mitchell.

With just seconds before the start of the third round, a cageside doctor spotted a cut to the eyelid of Thoresen, and a stoppage appeared imminent. Advised that further damage would end the fight, referee Herb Dean started the final frame, and a slugfest quickly broke out between the welterweights.

Mitchell again was the busier fighter, though Thoresen countered more effectively than before while landing a series of hard right hands. Exhausted, Mitchell shot for a takedown and wound up on his back with two minutes to work. He was unsuccessful, and Thoresen’s attempts to capitalize on top yielded little.

Judges scored the bout 30-27 in favor of Mitchell (12-2 MMA, 1-2 UFC), who after dual setbacks and several cancellations finds victory inside the octagon.

“This is the greatest night of my life,” he said. “I’ve been chasing this UFC win a long time. It means so much to me to win in the octagon. When Bruce Buffer said my name, all this emotion hit me. I kissed the canvas. … I don’t know what that was all about. This just means so much to me.”

Thoresen (17-4-1 MMA, 1-2 UFC) now has dropped back-to-back fights since a submission win over Besam Yousef in his octagon debut.